Separate ignition and battery inputs for FM radio

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luke.sleeman
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Separate ignition and battery inputs for FM radio

Post by luke.sleeman » Aug 14th, '17, 00:58

I just replaced my ancient tape deck/FM radio with a nifty Bluetooth/USB/FM unit. I got the new unit at Supercheap auto where it was on special.

There is only one problem - the old tape deck just had 2 power inputs: - 12v +ve and ground. This was wired to the boats switch panel where you could turn it on and off.

The new unit actually has 3 power inputs: battery +ve, ignition (accessories) +ve and ground. I've just joined the battery and ignition wire to the old 12v +ve and everything is fine - with the only exception being if I turn the unit off at the switchboard it forgets all its settings. Presumably it needs the battery power to store the settings while the 'cars' ignition is off.

Does anyone have any ideas for a good solution? At the moment all I can think of are 2 options: Never turn the radio off at the switch panel. Rewire the whole boat so that I can run bypass the switchboard for the radio and connect it to the battery just after the master cutoff switch.

Neither seem like great ideas.

Surely others have run into this problem? How do you solve it?

Luke



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Furstin
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Re: Separate ignition and battery inputs for FM radio

Post by Furstin » Aug 14th, '17, 07:32

Yep, I live with retuning to the station I want. Far from ideal.
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Jon
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Re: Separate ignition and battery inputs for FM radio

Post by Jon » Aug 14th, '17, 08:40

I don't have a solution.

Is this a common problem with the new head units because they are microprocessor driven? What do you look for in a new head unit to avoid this issue?

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luke.sleeman
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Re: Separate ignition and battery inputs for FM radio

Post by luke.sleeman » Aug 14th, '17, 09:02

Jon wrote:I don't have a solution.

Is this a common problem with the new head units because they are microprocessor driven? What do you look for in a new head unit to avoid this issue?
After some googling yes, it does seem common.

As for what to look for - Some units have memory that will work even without power (similar to the way a SD card doesn't need to be plugged in to keep the photos). I would suggest asking the sales person if the unit will remember the settings and channels even if the car battery goes flat or is removed.

Luke

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Re: Separate ignition and battery inputs for FM radio

Post by zebedee » Aug 14th, '17, 09:29

Measure the current consumed at the battery input with the unit off. Let us know the result...
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bachus
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Re: Separate ignition and battery inputs for FM radio

Post by bachus » Aug 14th, '17, 09:40

It is a cost competitive industry. Why add a non volatile memory chip to the design when in a car 12volt is always (almost) available. I suspect the Fusion brand does add the NVRAM but at a price.

Suggest you measure the current draw via the acc input when the radio is off (and when on just in case the current increases). You might be able to get a small battery pack to hold the memory depending on the current draw. Note on batteries. Alkaline might not be the best option if the current draw is real low. Alkaline are designed for heavy current over say "X" hours and will not provide N times "X" hours at lower current. You can buy AA holders on fleabay cheap. I would suggest a number of rechargeable Lithium Iron or similar AA equivalent size - 3 of them in a 3 battery holder. But then the recharger for these is special and adds another 60 bucks and the cost equation is disappearing I suspect. But measure the current draw. Then our collective heads can figure a solution.
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Re: Separate ignition and battery inputs for FM radio

Post by Bligh » Aug 14th, '17, 10:51

Something like this may do the job and serve as a backup supply too Charger
I have a bigger one that I use as an emergency pack in the car but it is compact and would be easy to fit and plug into the main supply to keep charged plus you can run other electronics off it such as phone, tablet etc.
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Re: Separate ignition and battery inputs for FM radio

Post by MoodyBlue » Aug 14th, '17, 11:30

Separate wire with a fuse, direct to the battery.

Keeping the memory does not draw enough power to cause issues.

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Re: Separate ignition and battery inputs for FM radio

Post by luke.sleeman » Aug 14th, '17, 16:54

zebedee wrote:Measure the current consumed at the battery input with the unit off. Let us know the result...
For somebody who has no idea how to use a multimeter (but has an old one stashed away in a box) how would I do this?

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Re: Separate ignition and battery inputs for FM radio

Post by bachus » Aug 14th, '17, 17:26

Jeff has answered already - current appears so small - just connect as he says. Your battery will probably have higher internal leakage than the current draw from the AUX connection (and your meter may not even measure the current if it is as low as I suspect).
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Re: Separate ignition and battery inputs for FM radio

Post by AZAmagnum » Aug 14th, '17, 20:50

could you hook up one of those small 9volt batteries, like the ones they use in smoke detectors ? ?

Just by the connector wires with the round male and female plugs. But where would you connect the negative wire ?
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Re: Separate ignition and battery inputs for FM radio

Post by sailboatmike » Aug 14th, '17, 21:43

I have same arrangement on my stereo unit, power draw in minimal at best, if your really worried one of those 1.5watt car battery maintainer solar panels would cover it I would think
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luke.sleeman
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Re: Separate ignition and battery inputs for FM radio

Post by luke.sleeman » Aug 15th, '17, 11:20

AZAmagnum wrote:could you hook up one of those small 9volt batteries, like the ones they use in smoke detectors ? ?

Just by the connector wires with the round male and female plugs. But where would you connect the negative wire ?
This is what I was thinking - but there are a lot of questions beyond my electrical skill:

* The unit requires 12v. Will 9v do for stand by?

* How will I wire it in? As you said, where does the black wire go? Just to the common ground?

* When the unit is running it apparently draws its main current from the battery connection. This isn't going to work if I only have a 9v battery there. I'm going to have to somehow also wire in the main power.

* Is it somehow possible to use a rechargeable 9v and have it charged while the main battery is on?

I suspect the answers to these questions are quite simple, however it's beyond my electrical skill to figure out!


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Re: Separate ignition and battery inputs for FM radio

Post by bachus » Aug 15th, '17, 11:45

Jeff's solution is still the simplest . . .
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Re: Separate ignition and battery inputs for FM radio

Post by luke.sleeman » Aug 15th, '17, 12:45

bachus wrote:Jeff's solution is still the simplest . . .
Yeah, wiring it directly into the battery is another option. Just due to where everything is positioned it's going to be a total pain. Perhaps I should just bite the bullet and do it. Or live with it loosing it's memory.

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Re: Separate ignition and battery inputs for FM radio

Post by bachus » Aug 15th, '17, 14:22

Ah understand now. Try a 9 volt battery. Quick to try. It may hold it up. Likely you will get the normal shelf life of the battery if it works if the current draw is as low as suspected.
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Re: Separate ignition and battery inputs for FM radio

Post by zebedee » Aug 15th, '17, 22:53

Do the specs for the unit specify a standby current?
It should be no more than about 20mA and possibly quite a bit less (insofar as 20mA has room for "quite a bit less").

I have a dim memory from the early 1990s of calculating that the GM-Holden spec of the day for maximum vehicle total parasitic (or standby) load was sufficient to completely flatten a car battery in about 3 months (2000 hours), and that the car should reliably start after up to 6 weeks with a fully charged healthy battery at the start. Given a typical car battery of about 40Ah, that would imply about 20mA maximum, and the radio manufacturers are likely to achieve no worse than that.

20mA over 6 weeks is 20Ah, which is enough to make a dent in your battery unless it is huge.

A load of 20mA would therefore be enough that a 9V battery or a small gellcell isn't really going to do the job. On the other hand, a small solar panel, even just 5W would be ample to keep it topped up.

In other news, I have a 10W solar panel which is surplus to requirements, free to a good home if you'd like it. If not, then free to someone else. Located near Moorabbin Airport. You'll need a basic voltage regulator to go with it.
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Re: Separate ignition and battery inputs for FM radio

Post by INMA » Aug 15th, '17, 22:59

Zebedee I will take the solar panel for my youngests solar project.
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Re: Separate ignition and battery inputs for FM radio

Post by zebedee » Aug 15th, '17, 23:10

Give Luke a chance to knock it back, in which case it is yours.
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Re: Separate ignition and battery inputs for FM radio

Post by luke.sleeman » Aug 16th, '17, 07:51

zebedee wrote:Give Luke a chance to knock it back, in which case it is yours.
It's fine, INMA can have it - I actually already have a panel the boat is plugged into while in storage. My main worry about wiring the unit directly into the battery is how much effort is going to be involved. The unit is on the opposite side of the boat to the battery. Most of the current set of wires are glued behind the carpet on the walls. So I'm either going to have to run some cable conduit and try and keep it kind of hidden, or I'm going to have to do some pretty drastic renovations to the carpet.

Fun fact - the original, original wires are fibreglassed to the hull. So it's impossible to change them in any way. I've got no idea which ones are still functional :?

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Re: Separate ignition and battery inputs for FM radio

Post by Johny » Aug 16th, '17, 13:56

I'd just make it a "taking the boat out" task along with rigging and everything else. Turn the radio on (at the panel), program it - use it. Turn it off when the boat isn't going to be used for a few days. If it came with a remote then just use that for hour to hour on/off.
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